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# Newton's Third Law

## For every action, there is an equal and opposite reaction.

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Rebuilding the Bridge

### Rebuilding the Bridge

Credit: Evonne
Source: http://www.flickr.com/photos/21761329@N03/5620411316

The Bay Bridge opened to traffic over 76 years ago. It has served as a connection between San Francisco and Oakland, carrying 240,000 vehicles per day. Consisting of 2 sections, an eastern and western portion, the bridge recently has been retrofitted to withstand possible upcoming earthquakes.

#### Amazing But True

• When the pressure from the wind pushes on the bridge, the bridge must push back with enough force to remain stable.
• The recent retrofit has been done to allow the bridge to withstand an earthquake of a magnitude 6.7 or greater.
• The swaying of the bridge is monitored my motion detectors which relay the information to a command center 2 hours away.
• The new bridge is designed to more like a sling, where the enormous force placed on the cable will be canceled out by the force on the road.

#### Can You Apply It?

Using the information provided above, answer the following questions.

1. In the new sling design, where would the forces be if a 100 ton vehicle was dropped on the bridge?
2. In total, how many separate ways can the bridge oscillate?

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